Method for the bleaching of kitchenware in a dishwasher

ABSTRACT

The invention provides a method for bleaching kitchenware in a dishwasher, comprising the step of the in situ activation of a bleach activator by means of a reactive oxygen species, where the reactive oxygen species is generated in situ in the dishwasher by electrolysis of an aqueous solution.

The invention relates to a method for bleaching kitchenware in adishwasher, and to the combination of a dishwasher with an electrolysiscell located outside of the dishwasher in the inflow line or with abattery-operated electrolysis cell located in the wash chamber.

For the bleaching of kitchenware such as crockery and cutlery, cleaningcompositions are usually used which comprise bleaches and/or bleachactivators (bleach precursors) in order to remove different types ofsoiling, in particular tea and coffee stains, from the kitchenware to becleaned. In this connection, the “actual” bleach, for example singletoxygen, is only formed in situ from the bleaches and/or bleachactivators used.

Examples of bleaches are hydrogen peroxide sources such as sodiumpercarbonate and sodium perborate, which form hydrogen peroxide in thepresence of water, and this in turn decomposes at temperatures above 60°C. to give water and singlet oxygen. When using hydrogen peroxidesources, the bleaching action thus only occurs at temperatures above 60°C.

Examples of bleach activators are acyl derivatives such astetraacetyl-ethylenediamine (TAED) and sodiump-nonanoyloxybenzenesulphonate (NOBS). The acyl derivative bleachactivators are used together with a hydrogen peroxide source. Followingrelease of the hydrogen peroxide from the hydrogen peroxide source, theacyl derivative bleach activators react with hydrogen peroxide with theformation of peroxycarboxylic acids. The peroxycarboxylic acidsgenerally disintegrate even at room temperature, with the formation ofthe carboxylic acid and singlet oxygen. Depending on the hydrogenperoxide source used, however, hydrogen peroxide is only released atrelatively high temperatures; for example, sodium percarbonate onlyforms hydrogen peroxide at temperatures above 50° C. in the presence ofwater. Consequently, in the case of the combination acyl derivativebleach activator/hydrogen peroxide source, the bleaching effect alsoonly occurs at relatively high temperatures, depending on the hydrogenperoxide source used.

Hydrogen peroxide and many peroxycarboxylic acids, for exampleperoxyacetic acid, are unstable and consequently non-storable, and cantherefore not be added directly to the dishwashing detergent.

DE10104470 and WO 2007/052064 describe customary cleaning compositionsfor use in dishwashers which can also comprise bleaches and/or bleachactivators.

U.S. Pat. No. 6,387,238 describes a method of producing an antimicrobialsolution comprising peroxyacetic acid. This method comprises theelectrolytic production of hydrogen peroxide, peroxide ions or peroxideradicals and the reaction of this species with an acetyl donor, with theformation of peroxyacetic acid. Example 1 describes the electrolytic(current strength: 5 A, current density: 100 mA/cm², voltage: 10 V)production of peroxyacetic acid.

WO 2006/117201 describes a method for cleaning, sterilizing anddisinfecting dishes and other kitchenware by means of a washing liquidwhere, as a result of the direct application of an electrical current toan electrode arranged in the washing liquid, said electrode being adiamond and/or lead/tin electrode, OH radicals are generated in thewashing liquid and these permit the cleaning, sterilizing anddisinfecting of the dishes and the other kitchenware. The currentdensity at the electrode is between 5 A/dm²(=500 mA/cm²) to 300 A/dm²(=30 A/cm²).

US 2002/023847 describes a method for producing a cleaning solution bymeans of electrolysis of water, and also an apparatus for the cleaningand sterilizing of objects such as dishes and clothing. The apparatuscomprises, for example, an electrolysis chamber with an ion exchangemembrane which separates the anode chamber from the cathode chamber. Thecathode chamber contains tap water, the anode chamber saltwater. Duringthe electrolysis, an aqueous solution of sodium hydroxide is formed inthe cathode chamber, and an aqueous solution of HOCl is formed in theanode chamber. The aqueous solution of sodium hydroxide is pumped fromthe cathode chamber and the objects to be cleaned are sprayed therewith.

JP 2003/211104 A describes a washing station which has a washing waterpreparation unit which comprises a cathode and an anode, where thesurface of at least one of the electrodes has conductive diamond. Oneexample of a washing station is a dishwasher (tableware scrubber). Inall cases, the “functional” water has sterilizing properties. Example 3describes the formation of an aqueous persulphate solution byelectrolysis (5 A, 120 cm², 15 min, 14 V) of a 0.6% strength aqueoussodium sulphate solution using diamond electrodes doped with boron.

WO 2009/067838 describes a method for the cleaning, sanitization,disinfection and odour neutralization of laundry, textiles, dishes,floor surfaces and vehicles with electrolyzed cold or warm water bymeans of oxidative radicals produced by boron-doped diamond electrodes.The cleaning intensities required for this purpose by means of oxidativeradicals can only be achieved with the help of diamond electrodes with 4volt overvoltage.

EP 1 944 403 describes a method for the work-up of washing water from acleaning installation, e.g. a washing machine, and for reusing theworked-up washing water in the cleaning installation, where the methodprovides, inter alia, a step in which the washing water to be worked upis treated electrochemically. In this step, organic constituents of thewashing water to be worked up, e.g. surfactants or soiling componentsare decomposed by means of ozone, hypochlorous acid (HOCl) or otheractive oxygen species. During the electrolysis, for example diamondelectrodes can be used, and a high voltage is applied so that highlyconcentrated ozone is formed.

US 2003/0414202 describes the production of electrolytic water by theelectrolysis of an alkaline electrolyte solution, where the electrolyticwater can be taken for cleaning and disinfection. The alkalineelectrolyte is a mixture of at least one electrolyte selected from thegroup consisting of sodium carbonate, potassium carbonate, phosphorussodium carbonate and sodium hypochlorite, and also a further electrolyteselected from the group consisting of sodium chloride, potassiumchloride, sodium bromide and potassium bromide. Nickel ferrite can beused as anode. The invention can be used in many applications, e.g. forthe cleaning and disinfection of warm water in public baths.

DE 103 36 588 A1 describes a method for the removal/decolouring ofcoloured substances/residues in liquids and from surfaces, in particularin dishwashers and in washing machines. In the method, the liquidcirculates continuously through channels between electrodes. In sodoing, the coloured molecules are anodically oxidized directly at theelectrode surface. In addition, “active” oxygen and “active” chlorineare formed at the electrode surfaces, and their accumulation likewisebrings about a removal/decolouring of coloured substances/residues inthe liquid and from surfaces. An anode made of titanium which has alayer of titanium oxide, for example, can be used as anode.

DE 10 2006 037 905 describes a dishwasher comprising an electrolysiscell for producing bleaches from the regenerating salt of a watersoftener. During the electrolysis, the salt solution producesoxidatively active substances (bleaches), in particular chlorine andsodium chlorite solution or potassium hypochlorite solution, dependingon the type of regenerating salt. Hydrogen gas and oxygen gas are formedas by-products. The electrodes consist preferably of corrosion-resistantmaterials, also with a catalytic coating, e.g. electrodes made oftitanium substrate with an oxidative coating of precious metal oxidesand precious metal dopings. In addition, however, it is also possible touse other electrode materials such as conductive diamond, platinum, tinoxide and stainless steels.

It was the object of the present invention to provide a method for thebleaching of kitchenware in a dishwasher which achieves excellentbleaching results even at temperatures of less than 45° C.

Moreover, the method according to the invention should be technicallyrealizable (no storage of unstable bleaches such as hydrogen peroxide orperoxycarboxylic acids) and economical (low electricity consumption),and also gentle as regards the dishwasher (no corrosion) and thekitchenware (no undesired discolorations).

This object is achieved by the method according to claim 1, and also bythe combinations in claims 21 and 22.

The method for bleaching kitchenware in a dishwasher of the presentinvention comprises the step of the in situ activation of a bleachactivator by means of a reactive oxygen species, where the reactiveoxygen species is generated in situ in the dishwasher by electrolysis ofan aqueous solution.

Dishwasher includes all types of dishwashers, i.e. both dishwashers forprivate households (domestic dishwashers) and also dishwashers that canbe used commercially (industrial and commercial dishwashers).

Kitchenware includes all types of kitchenware, for example crockery,cutlery, pots and glasses.

The reactive oxygen species is usually a reactive oxygen species whichhas at least one oxygen atom with the oxidation number −1. Examples ofreactive oxygen species which have at least one oxygen atom with theoxidation number −1 are hydrogen peroxide, hydrogen peroxide anions,perhydroxyl radicals, hydroxyl radicals, hyperoxide anions and ozone.

Preferably, the reactive oxygen species is selected from the groupconsisting of hydrogen peroxide, hydrogen peroxide anions, perhydroxylradicals and hydroxyl radicals. Particularly preferably, the reactiveoxygen species is selected from the group consisting of hydrogenperoxide, hydrogen peroxide anions and perhydroxyl radicals.

The reactive oxygen species is preferably generated by electrolysis ofthe water present in the aqueous solution.

The electrolysis can take place in an electrolysis cell comprising atleast one anode/cathode pair. The electrolysis cell can comprise oneanode/cathode pair or a plurality of serially connected anode/cathodepairs. Preferably, the electrolysis cell comprises a plurality ofserially connected anode/cathode pairs. The connection of theanode/cathode pairs can take place in a monopolar or bipolar manner. Abipolar connection is preferred.

The anode can comprise the following materials: carbon, for examplegraphite, glass carbon and electrically conductive diamond, preciousmetals, for example platinum and gold, metal oxides, for example iridiumoxide, chromium oxide, lead oxide, palladium oxide and ruthenium oxide,or mixed metal oxides.

Preferably, the anode comprises graphite, electrically conductivediamond or platinum.

Particularly preferably, the anode comprises materials with which a highoxygen overvoltage can be achieved, for example electrically conductivediamond or platinum.

The anode very particularly preferably comprises electrically conductivediamond.

Electrically conductive diamond is diamond which is doped with foreignatoms such that the diamond doped with foreign atoms conducts theelectrical current. Suitable foreign atoms are, for example, boron ornitrogen.

Preferably, the anode is an anode comprising electrically conductivediamond where the electrically conductive diamond is a diamond dopedwith boron.

Anodes comprising electrically conductive diamond usually comprise acarrier material, and the electrically conductive diamond.

Suitable as possible carrier materials are niobium, silicon, tungsten,titanium, silicon carbide, tantalum and graphite, and also ceramiccarrier materials such as titanium suboxide. Preferred carrier materialsare niobium, titanium and silicon. A particularly preferred carriermaterial is niobium.

The cathode can comprise the following materials: carbon, for examplegraphite, glass carbon and electrically conductive diamond, metals, forexample iron and nickel, steel, for example stainless steel, or preciousmetals, for example platinum.

The cathode very particularly preferably comprises electricallyconductive diamond or steel.

Preferably, the cathode is a cathode comprising electrically conductivediamond, where the electrically conductive diamond is a diamond dopedwith boron.

Cathodes comprising electrically conductive diamond usually comprise acarrier material, and the electrically conductive diamond.

Suitable as possible carrier materials are niobium, silicon, tungsten,titanium, silicon carbide, tantalum and graphite, and also ceramiccarrier materials such as titanium suboxide. Preferred carrier materialsare niobium, titanium and silicon. A particularly preferred carriermaterial is niobium.

Anodes or cathodes comprising electrically conductive diamond can beprepared by the CVD (“chemical vapour deposition”) method. Such diamondelectrodes are commercially available, such as for example from CondiasGmbH or Adamant-Technologies.

Anodes or cathodes comprising electrically conductive diamond can alsobe produced by the HTHP (“high temperature high pressure”) method. Inthis method, industrial diamond powder is incorporated mechanically intothe surface of a carrier metal sheet. Such diamond electrodes are alsocommercially available such as, for example, from pro aquaDiamantelektroden Produktion GmbH.

In one embodiment according to the invention, the anode comprisesboron-doped diamond, and the dishwasher housing comprising steel,preferably stainless steel, functions as cathode. In this embodiment,the dishwasher is thus part of the electrolysis cell.

Preferably, the dishwasher housing is not part of the electrolysis cell.

In a further, preferred embodiment according to the invention, both theanode and also the cathode comprise boron-doped diamond. This embodimenthas the advantage that the electrode polarity can be swapped, andpossible deposits on the electrodes can be removed. The electrodepolarity can be swapped, for example every 5 seconds to every 200minutes, or between the individual wash cycles.

Preferably, the electrolysis cell has an effective electrode surface(electrode size) of from 0.5 to 1000 cm², preferably from 1 to 500 cm²and particularly preferably from 2 to 100 cm². In this connection, theeffective electrode surface refers to the electrode surface of the anodeor of the anodes which comes into contact with the aqueous solutionduring the electrolysis and faces the cathode or the cathodes. If ananode is positioned between two cathodes (in the case of serialconnection of a plurality of anode/cathode pairs), then the effectiveelectrode surface of the anode or the anodes arises from the sum of theelectrode surfaces facing the cathodes.

In the preferred embodiment according to the invention, in which boththe anode and also the cathode comprise boron-doped diamond, theelectrodes are preferably of equal size, and therefore when swapping theelectrode polarities, the effective electrode surface remains the same.

The distance between the anode and the cathode is preferably 0.1 to 20mm, preferably 0.5 to 10 mm, particularly preferably 1 to 5 mm.

The anode and the cathode are preferably not separated from one anotherspatially, for example by a membrane.

Electrolysis cells which can be used are electrolysis cell types knownto the person skilled in the art such as divided or undivided flow cell,capillary gap cell or stacked-plate cell. A particularly preferredelectrolysis cell is the undivided flow cell.

The electrolysis cell can either be a built-in part of the dishwasher ora separate component.

If the electrolysis cell is a built-in part of the dishwasher, then theelectrolysis cell can, for example, be incorporated in the flooded areaof the washtub, preferably outside of the washing chamber, or theelectrolysis cell can be attached in the inflow line within thedishwasher, or the electrolysis cell can be integrated in an additionalwater circulation within the dishwasher.

A dishwasher which comprises an electrolysis cell, where theelectrolysis cell is integrated in an additional water circulationwithin the dishwasher, also forms part of this invention.

If the electrolysis cell is a separate component, then the electrolysiscell can, for example, be attached in the inflow line outside thedishwasher, for example in the fresh water feed between water tap anddishwasher, or be used as battery-operated electrolysis cell in thewashing chamber.

Dishwashers which are commercially available nowadays generally compriseno electrolysis cell as built-in part. It is therefore preferred thatthe electrolysis cell is used as a separate component. The electrolysiscell is particularly preferably a battery-operated electrolysis cellwhich is used in the washing chamber of the dishwasher.

A combination of a dishwasher with an electrolysis cell located outsidethe dishwasher in the inlet line also forms part of this invention.

A combination of a dishwasher with a battery-operated electrolysis celllocated in the washing chamber also forms part of this invention.

The electrolysis is carried out preferably at current densities, basedon the effective electrode surface, in the range from 0.5 to 1000mA/cm², particularly preferably in the range from 1 to 500 mA/cm², veryparticularly preferably in the range from 10 to 200 mA/cm² and mostpreferably in the range from 50 to 100 mA/cm²

The electrolysis is preferably carried out at current strengths of from0.02 to 30 A. A current strength in the range from 0.1 to 16 A isparticularly preferred, and very particular preference is given to acurrent strength in the range from 0.1 to 10 A.

The wash programs of a dishwasher usually include a wash cycle and arinse cycle. In the wash cycle, the ware is cleaned, while the rinsecycle serves to remove the rinse water and also to dry the ware. Thewash cycle can include two or more sub-wash cycles, for example one ormore pre-wash cycles and one or more main wash cycles.

The electrolysis can take place over the entire duration of thedishwasher program, but the electrolysis preferably takes place only inone or more time intervals during the dishwashing program. Preferably,the electrolysis takes place here in one or more time intervals beforeor during the wash cycle. The time intervals in which the electrolysistakes place can be between 5 seconds and 120 minutes, preferably between5 seconds and 60 minutes, particularly preferably between 1 minute and30 minutes, and in particular between 5 minutes and 15 minutes. Theelectrolysis takes place particularly preferably in a plurality ofintervals between 1 minute and 30 minutes, preferably between 5 minutesand 15 minutes, before or during the wash cycle.

The method according to the invention can be carried out at temperaturesin the range from 10 to 95° C., preferably in the range from 15 to 90°C., particularly preferably in the range from 20 to 65° C. and veryparticularly preferably in the range from 20 to 40° C., for example 30°C.

The method is preferably carried out at a temperature up to 60° C.,preferably up to 40° C., particularly preferably up to 30° C.

The aqueous solution is an aqueous solution which comprises electrolytesand thus conducts electrical current. Examples of aqueous solutionswhich comprise electrolytes and thus conduct an electrical current areaqueous solutions based on tap water.

The aqueous solution can comprise additives when carrying out theelectrolysis. However, the additives can also only be added to theaqueous solution while or after carrying out the electrolysis.

Examples of additives are the bleach activator, dishwashing detergents,rinse aids and regenerating salt.

A preferred additive is the bleach activator.

Bleach activators are usually compounds which react with reactive oxygenspecies, in particular with hydrogen peroxide, hydrogen peroxide anionsor perhydroxyl radicals, to give peroxycarboxylic acids or peroxyiminoacid. Both peroxycarboxylic acids and also peroxyimino acid candecompose with the formation of singlet oxygen.

The bleach activators which react with hydrogen peroxide to giveperoxycarboxylic acids can are preferably acyl derivatives.

The acyl radical of the acyl derivatives can have the following formula:

whereR¹ is C₁₋₂₀-alkyl or C₆₋₁₀-aryl,or

whereL¹ is C₁₋₂₀-alkylene or C₆₋₁₀-arylene.

Preferably, R¹ is C₁₋₁₀-alkyl or phenyl, particularly preferably R¹ isC₁₋₃-alkyl. Very particularly preferably, R¹ is methyl.

Preferably, L¹ is phenylene or naphthylene, particularly preferably L¹is phenylene. Preferably, formula (2) has the following formula

Acyl derivatives in which the acyl radical has formula (1) are preferredover acyl derivatives in which the acyl radical has formula (2).

Examples of C₁₋₃-alkyl are methyl, ethyl, n-propyl and isopropyl.C₁₋₁₀-alkyl can be unbranched or branched. Examples of C₁₋₁₀-alkyl aremethyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl,tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl and n-decyl,n-undecyl, n-dodecyl. C₁₋₂₀-alkyl can be unbranched or branched.Examples of C₁₋₂₀-alkyl are methyl, ethyl, n-propyl, isopropyl, n-butyl,sec-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl,n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-undecyl, n-dodecyl,n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl,n-octadecyl, n-nonadecyl and n-eicosyl (C₂₀).

C₆₋₁₀-aryl can be phenyl or naphthyl.

C₁₋₂₀-alkylene can be unbranched or branched. Examples of C₁₋₂₀-alkyleneare methylene, ethylene, propylene, isopropylene, butylene,sec-butylene, isobutylene, tert-butylene, pentylene, hexylene,heptylene, octylene, nonylene, decylene, undecylene, dodecylene,undecylene, dodecylene, tridecylene, tetradecylene, 2-decylbutylene,pentadecylene, hexadecylene, heptadecylene, octadecylene, nonadecyleneand eicosylene (C₂₀).

Examples of C₆₋₁₀-arylene are phenylene and naphthalene.

Examples of acyl derivative bleach activators are poly-O-acylatedpolyols, O-acylated phenol derivatives, carboxylic anhydrides,O-acylated hydroxylamines, O-acylated cyanuric acid derivatives,poly-N-acylated polyamines, N-acylated aniline derivatives,poly-N-acylated heterocycles comprising at least one nitrogen,N-acylated urea derivatives, N-acylated amides, N-acylated imides andN-acylated sulphonamides.

Examples of poly-O-acylated polyols are diacetyl glycol and triacetin,and also poly-O-acetylated sugar alcohols and sugars, for examplehexaacetylsorbitol, hexaacetylmannitol, pentaacetylglucose,tetraacetylxylose and octaacetyllactose, and alsotetraacetylgluconolactone.

Examples of O-acylated phenol derivatives are sodiump-nonanoyloxybenzenesulphonate (NOBS), sodiump-isononanoyloxy-benzenesulphonate, sodiump-benzoyloxybenzenesulphonate, sodium p-nonanoyloxybenzoate, and sodiump-decanoyloxybenzoate.

Examples of carboxylic anhydrides are phthalic anhydride and benzoicanhydride.

Examples of O-acylated hydroxylamines areO-benzoyl-N,N-succinylhydroxylamine, O-acetyl-N,N-succinylhydroxylamineand O,N,N-triacetylhydroxylamine.

Examples of O-acylated cyanuric acid derivatives are triacetylcyanuricacid and tribenzoylcyanuric acid.

Examples of poly-N-acylated polyamines are tetraacetylmethylenediamine,tetraacetylethylenediamine (TAED) and tetraacetylhexylenediamine.

One example of a N-acylated aniline derivative is N,N-diacetylaniline.

Examples of poly-N-acylated heterocycles comprising at least onenitrogen are 1,3-diacetyl-5,5-dimethylhydantoin, tetraacetylglucoluril,1,5-diacetyl-2,2-dioxo-hexahydro-1,3,5-triazine,1,5-diacetyl-2,4-dioxohexahydro-1,3,5-triazine,1,5-diacetyl-2,4-dioxohexahydro-1,3,5-triazine,1,4-diacetyl-2,5-diketopiperazine, 1,3-diacetyl-4,5-diacetoxyimidazolineand monoacetylmaleic acid hydrazide.

One example of an N-acylated urea derivative istetraacetylpropylenediurea.

One example of an N-acylated amide is benzoylcaprolactam.

One example of an N-acylated imide is N-nonanoylsuccinimide.

Examples of N-acylated sulphonamides are N-methyl-N-mesylacetamide,N-methyl-N-mesylbenzamide, N,N′-dimethyl-N,N′-diacetylsulphurylamide andN,N′-diethyl-N,N′-dipropanoylsulphurylamide.

Bleach activators which react with hydrogen peroxide to give peroxyiminoacid can be ammonium nitriles, for example N-methylmorpholiniumacetonitrile hydrogen sulphate, trimethylammonium acetonitrile hydrogensulphate.

Bleach activators which react with hydrogen peroxide to giveperoxycarboxylic acids are preferred. Particularly preferred bleachactivators are acyl derivative bleach activators. Very particularlypreferred bleach activators are poly-N-acylated polyamines. Aparticularly preferred bleach activator is tetraacetylethylenediamine(TAED).

The concentration of the bleach activator in the aqueous solution can be0.001 to 10% by weight, preferably 0.01 to 5% by weight, particularlypreferably 0.02 to 1% by weight, based on the weight of the aqueoussolution.

The bleach activator can be part of the dishwashing detergent.

The dishwashing detergent can comprise the constituents customary for adishwashing detergent, for example water softeners, bleaches, bleachactivators, bleach catalysts, bleach stabilizers, surfactants andenzymes. Moreover, the dishwashing detergent can also comprise foaminhibitors, corrosion inhibitors and fillers.

Examples of water softeners are pentasodium triphosphate, sodiumcarbonate, sodium hydrogencarbonate, soap, zeolites, and complexingagents such as ethylenediaminetetraacetic acid (EDTA). Pentasodiumtriphosphate or zeolite are the preferred water softeners.

Examples of bleaches are “oxygen-based” bleaches, and also“chlorine-based” bleaches.

Customary “oxygen-based” bleaches are hydrogen peroxide sources.Examples of hydrogen peroxide sources are alkali metal perborates, forexample sodium perborate and alkali metal percarbonates, for examplesodium percarbonate, alkali metal persulphates, for example potassiummonopersulphate, alkali metal persilicates and alkali metalperphosphates.

One example of a “chlorine-based” bleach is sodium hypochlorite.

“Oxygen-based” bleaches are preferred, in particular sodium perborateand sodium percarbonate. The most preferred bleach is sodiumpercarbonate.

Examples of bleach stabilizers are phosphonates.

Examples of surfactants are anionic surfactants, for example linearalkylbenzenesulphonates, secondary alkanesulphonates, fatty alcoholsulphates and methyl ester sulphates, and non-ionic surfactants, forexample fatty alcohol polyglycol ethers and sugar surfactants.

Examples of enzymes are amylases, lipases and proteases.

Examples of foam inhibitors are silicone oils and paraffin oils.

One example of a corrosion inhibitor is sodium metasilicate.

One example of a filler is sodium sulphate.

The regenerating salt is sodium chloride.

Particularly preferred additives are water softeners, bleach activator,surfactants and enzymes.

The pH of the aqueous solution is preferably in the range from 2 to 13,particularly preferably in the range from 3 to 12, and very particularlypreferably in the range from 6 to 11.

Preferably, for the method according to the invention, a degree of soilremoval for bleachable soilings, for example tea, of at least 20%,preferably at least 50%, is achieved.

The degree of soil removal is determined as follows:

The determination takes place by soiling a white melamine resinreference substrate firstly under standard conditions (the followingwere used: DM 11 Tea Serie 096, 2.4 cm×3.9 cm) and subjecting it to areflection measurement at 460 nm before and after carrying out thetreatment with the aqueous solution. The soil removal is calculated in %from the reflectance values R before and after carrying out the methodand also the reflectance value of a white melamine resin referencesubstrate according to the following formula:

${{Degree}\mspace{14mu} {of}\mspace{14mu} {soil}\mspace{14mu} {{removal}\mspace{14mu}\lbrack\%\rbrack}} = {\frac{{R( {{after}\mspace{14mu} {cleaning}} )} - {R( {{before}\mspace{14mu} {cleaning}} )}}{{R( {{white}\mspace{14mu} {melamine}\mspace{14mu} {resin}} )} - {R( {{before}\mspace{14mu} {cleaning}} )}} \times 100}$

All of the measurements here are carried out five times and the averageis given. The following values were measured for the white melamineresin reference substrate and the standardized melamine substrate DM11:

R (white reference): 0.81

R (DM11 Tea Serie 096): 0.47

The reflectance measurements are carried out using a spectrophotometer,make Gretag Macbeth, model Spectrolino, under the following conditions:observation angle 10°, type of light D65, UV filter.

The method according to the invention is characterized in that it isexceptionally suitable for the bleaching of kitchenware in a dishwasher,where the method has a very good bleaching effect even at temperaturesof less than 45° C.

The method according to the invention is also technically realizable (nostorage of unstable bleaches such as hydrogen peroxide orperoxycarboxylic acids) and economical (low electricity consumption) andalso gentle with regard to the dishwasher (no corrosion) and thekitchenware (no undesired decolourations).

Furthermore, the method can exhibit positive accompanying effects, suchas the decolouring of the aqueous solution and also disinfection,cleaning and odour neutralization of the kitchenware to be bleached.

FIG. 1 shows the schematic representation of the experimental apparatusused in the examples.

EXAMPLES Experimental Set-Up

The experiments are carried out in a 1000 ml jacketed vessel made ofglass with mechanical stirrer (IKA stirrer motor with glass stirrer andmovable PTFE stirrer blade) and liquid circulation (Iwaki magnetic pumpMD6-230GS01, 80-90 l/h) and an electrolysis cell with boron-dopeddiamond electrodes (Adamant miniDiaCell, diamond on silicon, 12.5 cm²electrode area). FIG. 1 shows a schematic representation of theexperimental apparatus.

The test substrates are made of melamine resin (DM 11 Tea Serie 096, 2.4cm×3.9 cm).

The following aqueous solutions are used:

Aqueous solution A: 700 g of demin. water, 10 g of NaHCO₃Aqueous solution B: 700 g of demin. water, 10 g of NaHCO₃, 0.18 g ofTAEDAqueous solution C: 700 g of demin. water, 10 g of NaHCO₃, 0.18 g ofTAED, 0.32 g of H₂O₂ solution (30% of H₂O₂ in water).

TAED stands for tetraacetylethylenediamine. Demin. water stands fordemineralized and completely deionized water.

The selected concentration of TAED in the aqueous solutions B and Ccorresponds to that of standard commercial dishwashing detergents. Inthe aqueous solution C, the molar ratio of H₂O₂/TAED is 4:1.

Comparative Examples C1 to C3

The aqueous solutions A (C1), B (C2), and C(C3) are provided in theexperimental apparatus. The test substrates are introduced into thejacketed vessel such that they immerse completely into the aqueoussolution and are wetted by it. The aqueous solutions are circulated bypumping for 30 minutes at 40° C. without electrolysis. The testsubstrates are removed from the experimental apparatus, rinsedthoroughly with demin. water and dried with the exclusion of light.

Example 1

The aqueous solution B is provided in the experimental apparatus. Thetest substrate is introduced into the jacketed vessel such that itimmerses completely into the aqueous solution and is wetted by it. Theaqueous solution B is circulated in the experimental apparatus bypumping for 30 minutes at 40° C. with electrolysis (1.2 A). The testsubstrate is removed from the experimental apparatus, rinsed thoroughlywith demin. water and dried with the exclusion of light.

Example 2

The aqueous solution B is provided in the experimental apparatus. Thetest substrate is introduced into the jacketed vessel such that itimmerses completely into the aqueous solution and is wetted by it. Theaqueous solution B is circulated in the experimental apparatus bypumping for 30 minutes at 60° C. with electrolysis (1.2 A). The testsubstrate is removed from the experimental apparatus, rinsed thoroughlywith demin. water and dried with the exclusion of light.

Example 3

The aqueous solution A is circulated in the experimental apparatus bypumping at 40° C. with electrolysis (1.2 A) for 10 minutes without testsubstrate. The current source is switched off. 0.18 g of TAED and thetest substrate are added and the resulting aqueous solution iscirculated by pumping at 40° C. for a further 30 minutes without theapplication of current. The test substrate is removed from theexperimental apparatus, rinsed thoroughly with demin. water and driedwith the exclusion of light.

Example 4

The aqueous solution A is circulated in the experimental apparatus bypumping at 60° C. with electrolysis (1.2 A) for 10 minutes without testsubstrate. The current source is switched off. 0.18 g of TAED and thetest substrate are added and the resulting aqueous solution iscirculated by pumping at 60° C. for a further 30 minutes without theapplication of current. The test substrate is removed from theexperimental apparatus, rinsed thoroughly with demin. water and driedwith the exclusion of light.

Determination of the Degree of Soil Removal

The soil removal is determined by subjecting the test substrate made ofmelamine resin to a reflection measurement at 460 nm before and afterthe treatment with the aqueous solution. The soil removal was calculatedin % from the reflectance values R before and after the treatment, andalso the reflectance value of a white reference substrate made ofmelamine resin according to the following formula:

${{Soil}\mspace{14mu} {{removal}\mspace{14mu}\lbrack\%\rbrack}} = {\frac{{R( {{after}\mspace{14mu} {cleaning}} )} - {R( {{before}\mspace{14mu} {cleaning}} )}}{{R( {{white}\mspace{14mu} {substrate}} )} - {R( {{before}\mspace{14mu} {cleaning}} )}} \times 100}$

The reflectance measurements are carried out using a spectrophotometer,make Gretag Macbeth, model Spectrolino, under the following conditions:observation angle 10°, type of light D65, UV filter.

The test substrates of the Comparative Examples C1 to C3, and also ofExamples 1 to 4 have the following degree of soil removal following thetreatment:

TABLE 1 Example Temperature [° C.] Soil removal [%] C1 40 21 C2 40 25 C340 48 1 40 60 2 60 67 3 40 50 4 60 70

The pure washing effect of aqueous solution A brings about a soilremoval of 21% (C1). The addition of TAED (C2) leads, as expected, onlyto a slight improvement in the soil removal to 25%. Likewise asexpected, as a result of adding H₂O₂ (C3), the bleach precursor (TAED)is activated, such that a soil removal of 48% is achieved.

Example 1 shows that, at 40° C. and with the same amount of TAED, usingthe method according to the invention a higher soil removal (60%) can beachieved than with the comparative method C3 (48%). Example 2 shows thatthe soil removal increases to 67% as a result of increasing thetemperature to 60° C.

Examples 3 and 4 show that it is also possible to first activate theaqueous solution electrolytically for 10 minutes, and then to add TAED.It is thus possible to achieve a very good soil removal with a lowercurrent input.

1.-22. (canceled)
 23. A method for bleaching kitchenware in adishwasher, comprising the step of the in situ activation of a bleachactivator by means of a reactive oxygen species, where the reactiveoxygen species is generated in situ in the dishwasher by electrolysis ofan aqueous solution.
 24. The method according to claim 23, where thereactive oxygen species is a reactive oxygen species which has at leastone oxygen atom with the oxidation number −1.
 25. The method accordingto claim 24, where the reactive oxygen species is selected from thegroup consisting of hydrogen peroxide, hydrogen peroxide anions,perhydroxyl radicals and hydroxyl radicals.
 26. The method according toclaim 23, where the electrolysis takes place in an electrolysis cellcomprising at least one anode/cathode pair.
 27. The method according toclaim 26, where the anode comprises electrically conductive diamond. 28.The method according to claim 27, where the anode comprises diamonddoped with boron.
 29. The method according to claim 26, where thecathode comprises diamond doped with boron.
 30. The method according toclaim 26, where the electrolysis cell is a built-in part of thedishwasher.
 31. The method according to claim 26, where the electrolysiscell is a component separate from the dishwasher.
 32. The methodaccording to claim 31, where the electrolysis cell is attached in theinflow line outside of the dishwasher, or is used as battery-operatedelectrolysis cell in the wash chamber.
 33. The method according to claim23, where the electrolysis is carried out at current densities in therange from 10 to 200 mA/cm2.
 34. The method according to claim 23, wherethe electrolysis is carried out at current densities in the range from0.1 to 16 A.
 35. The method according to claim 23, where theelectrolysis takes place in one or more time intervals from 1 minute to30 minutes, before or during the wash cycle.
 36. The method according toclaim 23, where the method is carried out at temperatures in the rangefrom 20 to 65° C.
 37. The method according to claim 23, where theaqueous solution comprises additives while carrying out theelectrolysis, or additive are added to the aqueous solution aftercarrying out the electrolysis.
 38. The method according to claim 37where the bleach activator is one of the additives.
 39. The methodaccording to claim 23, where the bleach activator is an acyl derivative,the acyl radical of which has the following formula:

where R¹ is C₁₋₂₀-alkyl or C₆₋₁₀-aryl, or

where L¹ is C₁₋₂₀-alkylene or C₆₋₁₀-arylene.
 40. The method according toclaim 23, where the bleach activator is a poly-N-acylated polyamine. 41.The method according to claim 23, where the bleach activator istetraacetylethylenediamine (TAED).
 42. The method according to claim 23,where the pH of the aqueous solution is in the range from 3 to
 12. 43. Acombination of a dishwasher with an electrolysis cell located outside ofthe dishwasher in the inflow line.
 44. A combination of a dishwasherwith a battery-operated electrolysis cell located in the wash chamber.45. The method according to claim 23, where the electrolysis is carriedout at current densities in the range from 50 to 100 mA/cm2.
 46. Themethod according to claim 23, where the electrolysis is carried out atcurrent densities in the range from 0.1 to 10 A, the electrolysis takesplace in one or more time intervals from 5 minutes to 15 minutes beforeor during the wash cycle, the method is carried out at temperatures inthe range from 20 to 40° C., and the pH of the aqueous solution is inthe range from 6 to 11.